Leonard Downie Jr. said yesterday he is stepping down as The Washington Post's executive editor, ending a 17-year tenure in which the paper became a major online force and won a slew of prizes for high-profile investigations, including one that Downie published over President Bush's objections.

Downie, 66, said his last day will be Sept. 8. The paper's new publisher, Katharine Weymouth, said she plans to announce a successor soon.

"After 44 years, the notion of not working in the newsroom anymore brings a lot of emotions," Downie said in an interview. "I will really miss it. . . . At the same time I'm ready to do this, because so much further change now needs to take place at the newspaper and Web site, and someone else should be tackling that."

He summed up his management philosophy in a sentence: "You hire people smarter and more talented than you and enable them to do their best work."

Associate Editor Robert G. Kaiser, Downie's first managing editor, called him "the straightest shooter I ever had to deal with. One of my anxieties about my friend is that his qualities won't be appreciated because they're so invisible. . . . It's never occurred to him to seek the spotlight or be flashy or sexy or any of the things that seem to be so valued now. He's a really large figure who's accomplished so much, but without any hint of charisma in the wider world."

Downie will become a Post Co. vice president at large, a title also held by his predecessor as editor, Ben Bradlee.

An Ohio native who spent his entire career at The Post, Downie has helped shape the paper for nearly a quarter-century, first when he became managing editor in 1984 and more forcefully after succeeding Bradlee in 1991. Unlike Bradlee, he has largely avoided television and the party circuit. Downie said he and Post Co. chief executive Donald Graham, who followed his mother, Katharine Graham, in the publisher's job, occasionally talked about how "we were both known as the colorless successors to colorful people."

Graham said in an interview that he chose Downie "because I knew his day-to-day news judgment was superb, that he had a ferocious sense of fairness, that he had great taste in news people, and because he worked incredibly hard. He was always honest with everyone on the paper and with the people we covered."

Addressing a packed newsroom yesterday, Downie said, "I love all of you -- and I love our newspaper." But he said his Post work "has often crowded my personal life" and that he wants to spend more time with his wife, Janice. Downie seemed moved by three sustained ovations.

Weymouth told the staff: "Len is incontrovertibly one of the great editors of our time. He has guided The Washington Post with a steady and unerring hand. We all -- those of us who work here as well as our readers -- have benefited enormously from having him here. Len never let himself be intimidated by the shadow of Ben's legacy. He brought his own style of leadership."

Downie led the newsroom to 25 Pulitzer Prizes, including three gold medals for public service, and The Post won six of the awards in April, one shy of the annual record. The list includes a 2005 prize for disclosing the existence of secret CIA prisons in Eastern Europe used to interrogate terror suspects, despite a White House meeting at which Bush asked that the story be killed.

Downie's mantra -- reflected in routine stories as well as such Pulitzer-winning efforts as the 2007 exposé of shoddy conditions at Walter Reed Army Medical Center -- was "accountability journalism."

Bob Woodward, the paper's best-known investigative reporter, said in an interview that he grew accustomed to Downie's "notorious pencil marks all over a draft story." He said Downie resisted pressure from several administrations on national security stories but also never hesitated to hold a story he found incomplete, deferring a decision until more information could be gathered.

"Never once did I find his caution frustrating," Woodward said. "He always had good questions."

Downie correctly guessed -- on the third try -- the identity of Woodward's secret Watergate source, Deep Throat, but Woodward did not confirm it for him until 2005, when former FBI official Mark Felt became ill.

Columnist Eugene Robinson said that when he ran the Style section, Downie always told him what he liked and disliked, "and if we pushed too far, he'd let me know. I would get a phone call late at night if I miscalibrated Len's tolerance for envelope-pushing." But he said he was allowed to pursue an idea that Downie found "crazy" -- tapping financial reporter David Segal as pop music critic -- and that Downie later admitted Robinson had been right.

Sandra Sugawara, the assistant managing editor for business news, said: "He was able to cut through a lot of the white noise and figure out what the heart of the story was. . . . He'd be able to tell you he disagreed with you and why, but in a very non-emotional way. I found it very easy to take."

Downie presided over a gradual expansion of The Post, especially in suburban coverage, including weekly sections tailored to Maryland and Virginia counties. But in the past five years he has managed three rounds of early-retirement buyouts, forced by declining circulation and revenue, that cut the newsroom from the equivalent of 900 full-time staffers to just under 700.

"Rather than whine about it, we roll up our sleeves and demonstrate we have really talented people in our newsroom to perform great journalism," he said. As for the Web, Downie said he "was slow to understand its importance" but came to realize it could broaden the reach of The Post's journalism. While the paper's circulation has declined from 813,000 to 673,000 since 2000, washingtonpost.com has grown to draw 9.4 million unique visitors each month.

A hands-on, consensus-building manager who spends part of each day on the newsroom floor, where his raucous laugh sometimes echoes above the din, Downie prides himself on assembling a meritocracy. He is sometimes criticized for micromanaging but has never been accused of fostering a star system.

Downie is almost never heard raising his voice, but as a reporter, he recalled, he had "a slow-building temper" and "allowed it to erupt against my superiors. I had to learn to tame that."

Female staffers say he was open to part-time and flexible arrangements before such practices were widely accepted, and he routinely named women to head major desks, including National, Style, Metro and Business.

The son of a businessman whose career included work as a Cleveland milkman, Downie started at The Post as a 1964 summer intern, recalling later that he felt "very provincial" because the other interns had famous or well-connected parents. The Ohio State University graduate soon became a Metro reporter specializing in investigations of urban problems. One series on flaws in the District's court system led to the creation of D.C. Superior Court; another, implicating savings and loan executives in real estate scams, prompted banks to pull $1 million in advertising from the paper. Downie recalled that Bradlee didn't want to hear about the details, saying: "Just get it right, kid."

After becoming a Metro desk editor against his wishes, Downie wound up supervising much of the paper's Watergate coverage by Woodward and Carl Bernstein, and he became assistant managing editor for local news in 1974. Five years later he was named London bureau chief, and he returned to Washington as national editor in 1982.

The decisions he has made over the years reflect a dizzying range of journalistic challenges. In 1992 he delayed until after the election a report on then-Sen. Bob Packwood (R-Ore.) making unwanted sexual advances toward 10 female employees and lobbyists, drawing criticism despite his insistence that the story had not been ready earlier. In 1994 he delayed publication of a story on Paula Jones's sexual allegations against President Bill Clinton until the day before she filed a civil suit against Clinton. In 1996 he decided against reporting that Republican presidential nominee Bob Dole had had an affair 28 years earlier, news that later leaked to the National Enquirer.

Downie has also had to deal with plagiarism, sexual harassment and racial tensions in the newsroom.

In 1995 he helped decide that The Post would join the New York Times in publishing, at the request of federal officials, a 35,000-word manifesto by the serial killer known as the Unabomber.

More recently, Downie decided in 2004 to publish the F-word after Vice President Cheney used it in a dust-up with Sen. Patrick Leahy (D-Vt.). In 2005 he publicly chided Woodward for not disclosing to him that an administration official had told the reporter the identity of CIA operative Valerie Plame 2 1/2 years earlier.

Downie's values as an editor were forged in his days as a muckraking reporter. "Investigative reporting is tedious and scary," he said. "The people you're investigating don't like you. Sources are scared to death to talk to you. And many times your colleagues don't like you because you're investigating someone on their beat."

Perhaps the paper's greatest shortcoming during Downie's tenure came during the run-up to the Iraq war. He later took responsibility for not giving more front-page attention to critics of Bush's case for the war.

"One of my failings is that while I delegate a lot, I also stick my finger in everything we do," Downie said. While The Post pursued some skeptical reporting about the rationale for invading Iraq, "I didn't pounce on it and bring it to the fore as a high priority. That antenna I normally had just didn't function well enough."

Downie's retirement has been the subject of speculation for months as Weymouth, who became publisher in February, has met with numerous editors about the paper's future. Those considered to be the strongest contenders for his job are Post Managing Editor Philip Bennett, former Wall Street Journal managing editor Marcus Brauchli and Jonathan Landman, a New York Times deputy managing editor.

Downie said he also plans to write books -- his novel, "The Rules of the Game," is due out in January -- and become an advocate for improving journalism.